Metallic electro-migration has long been recognized as a significant failure mode in many electrical and electronic systems. It is widely believed that there are two types of electro-migration: electrolytic and solid state. The solid-state electro-migration is electron momentum transfer by nature, while the electrolytic electro-migration transfer is ionic, e.g., the metal is transferred in its ionic form.
Certain oxygen generators and fuel cells are electrochemical devices, examples of which are shown in U.S. Pat. Nos. 5,985,113; 5,871,624 and 6,194,335. These three patents are incorporated herein by reference. Oxygen generators of this type are used in some Integrated Manifold and Tube (IMAT) modules. The IMAT module has emerged as an attractive configuration for electrically driven oxygen separation due largely to the ability to make numerous series electrical connections while minimizing the number of large-area seals. These series connections include a bare region of ceramic electrolyte material separating two conductive regions at different electrical potentials.
IMAT modules are moving toward the direction of lower operation temperature, compared to traditional operation temperatures around 1000° C. One of the advantages of operating at 750° C. or lower is enabling use of silver in electrode and/or current collector instead other noble metals such as platinum. Thus the cost of these systems can be significantly reduced. However, as one of the most conductive metals, silver is also particularly susceptible to electro-migration. To date, experiments of silver migration on solid-state electrochemical devices have pointed toward electrolytic migration.
Silver electro-migration is enough of a problem that the life of IMAT for oxygen generation is limited because of reduced oxygen flow rate due to silver migration. Migration of the silver eventually produces failures by shorting across the inter-conductor spacing.
It is a principal object of the present invention to prevent shorts between silver conductors caused by electro-migration.